Data transmission network

ABSTRACT

Data transmission network having a least one line termination device connected via a data transmission medium to several network termination devices, each network termination device comprising a request message generator for generating a data transmission request message when a data communication device connected to the network termination device is sending data, and an xDSL transceiver for transmitting an upstream data frame including the generated request message via the data transmission medium to the line termination device. The line termination device includes a selection unit for selecting network termination devices which have sent a request message depending on stored status information data of the network termination devices, a grant message generator for generating data transmission grant messages for the selected network termination devices, and an xDSL transceiver for broadcasting downstream data frames including the generated grant messages via the data transmission medium to the network termination devices.

The present invention refers to a data transmission network and a methodfor data transmission which allow xDSL data transmission and voice datatransmission between a backbone network and a network termination deviceon any data transmission medium such as a copper telephone line.

BACKGROUND

FIG. 1 shows a data transmission network according to the state of theart. An IP backbone is connected via a broad-band data transmission lineto a main switch such as an xDSL line termination device. The mainswitch is connected to several xDSL network termination devices NT overxMII interface. The NT is connected via a UTP telephone line to a localswitch or hub which distributes the data packages received from the mainswitch to different data communication devices such as a personalcomputer or a laptop or an IP phone via a CAT5 communication line. Theswitch and the data communication devices form a local area network(LAN), e.g. an Ethernet local area network. The Ethernet local areanetwork according to the state of the art does not allow data exchangebetween data communication devices and the local switch via an ordinaryCAT3 copper telephone line over home telephone topology which requiresits own wiring structure besides the telephone lines which are alreadyinstalled in a building.

SUMMARY

It is a main object of the present invention to provide a datatransmission network and a method for data transmission which allow xDSLdata exchange and a voice data exchange on any data transmission mediumand in particular on an ordinary POTS telephone line. (POTS: Plain OldTelephone Service).

The data transmission network according to the invention has at leastone line termination device (LT) connected via a data transmissionmedium to several network termination devices NT.

Each network termination device (NT) comprises

a request message generator for generating a data transmission requestmessage when a data communication device connected to the networktermination device is sending data, and

an xDSL transceiver for transmitting an upstream data frame includingthe generated request message via the data transmission medium to theline termination device;

said line termination device comprising

a selection unit for selecting network termination devices which havesent a request message depending on stored status information data ofthe network termination devices,

a grant message generator for generating data transmission grantmessages for the selected network termination devices, and

an xDSL transceiver for broadcasting downstream data frames includingthe generated grant messages via the transmission medium to the networktermination devices.

In a preferred embodiment, the data transmission medium is the telephoneline, preferably a UTP copper telephone line.

In a preferred embodiment of the data transmission network, the datatransmission request message comprises a request message opcode and anumber of time slots required for data transmission of the data sent bythe data communication device.

In a preferred embodiment of the data transmission network, a datatransmission grant message comprises a grant message opcode and anaddress of the selected network termination device.

In a still further preferred embodiment of the data transmission networkaccording to the present invention, the upstream data frames are sentfrom the network termination devices to the line termination device viathe data transmission medium in an upstream frequency band, and thedownstream data frames are sent from the line termination device to thenetwork termination devices via the data transmission medium in adownstream frequency band.

The downstream frequency band ranges preferably between 1 and 3 MHz, andthe upstream frequency band ranges Preferably between 4 and 8 MHz.

The line termination device comprises in a preferred embodiment an MIIinterface for connection to a switch.

Each data frame comprises in a preferred embodiment

a synchronization data field,

the message data field,

a payload data field, and

an error correction data field.

In a preferred embodiment, each network termination device is connectedto a passive signal splitter.

The passive signal splitter comprises preferably a low-pass filter forfiltering a telephone signal and a high-pass filter for filtering anxDSL data signal.

In a preferred embodiment, the line termination device comprises storingmeans for storing the information data of the different networktermination devices connected to the line termination device.

In a preferred embodiment, the storing means stores the addresses of thenetwork termination devices and the corresponding numbers of requiredtime slots received from the network termination devices in a requestmessage.

In a still further preferred embodiment of the data transmission networkaccording to the present invention, the selection unit of the linetermination device reads the status information data stored in thestoring means, selects the network termination devices for datatransmission according to a programmed selection algorithm and activatesthe grant message generator for generating grant messages for theselected network termination devices.

In a preferred embodiment, the xDSL transceiver of the line terminationdevice includes an adaptive gain control circuit and an equalizer.

The line termination device comprises preferably

first storing means for storing the automatic gain control coefficientsand the network termination devices connected to the line terminationdevice and

second storing means for storing equalizer coefficients for the networktermination devices connected to the line termination device.

The automatic gain control coefficients of the network terminationdevice selected by the selecting unit are loaded into the automatic gaincontrol circuit of the xDSL transceiver of the line termination device.

The equalizer coefficients of the network termination device selected bythe selecting unit are loaded preferably into the equalizer of the xDSLtransceiver of the line termination device.

In a preferred embodiment of the data transmission network according tothe present invention, the network termination device comprises a grantdecoder for decoding messages within downstream data frames broadcastedby the line termination device.

In a preferred embodiment, the xDSL transceiver of the line terminationdevice and the network termination devices are VDSL transceivers.

In a preferred embodiment, the impedances of the network terminationdevices connected to the data transmission medium are balanced.

In a preferred embodiment of the data transmission network according tothe present invention, at least eight network termination devices areconnected via the data transmission medium to the line terminationdevice.

In a preferred embodiment of the data transmission network, several linetermination devices are connected to a switch.

In a preferred embodiment of the data transmission network, the switchis connected to an IP backbone.

The invention further provides a method for data transmission comprisingthe following steps:

generating a data transmission request message by a network terminationdevice when the network termination device receives data from aconnected data communication device,

transmitting the generated data transmission request message within anupstream data frame via a data transmission medium to a line terminationdevice while getting a grant message,

selecting the network termination devices depending on the stored statusinformation data of the network termination devices,

generating data transmission grant messages for the selected networktermination devices by the line termination device,

broadcasting downstream data frames containing the generated grantmessages via the data transmission medium to the network terminationdevices, and

transmitting data from the selected network termination device after thegrant message has been decoded.

In the following, preferred embodiments of the data transmission networkand the data transmission method according to the present invention aredescribed in detail with respect to the enclosed Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a data transmission network according to the state of theart;

FIG. 2 shows a data transmission network according to the presentinvention having a topology as found in the United States of America;

FIG. 3 shows a data transmission network according to the presentinvention having a topology as found in Europe and in Asia;

FIG. 4 shows a block diagram of a line termination device according tothe present invention;

FIG. 5 shows a network termination status table stored within a linetermination device;

FIG. 6 shows a block diagram of a network termination device accordingto the present invention;

FIGS. 7 a, 7 b show a request message and a grant message in principle;

FIG. 8 shows a flowchart of the operation within a line terminationdevice;

FIG. 9 shows a flowchart of the operations within the networktermination device according to the invention.

DETAILED DESCRIPTION

FIG. 2 shows a preferred embodiment of a data transmission network 1according to the present invention. The data transmission network 1 asshown in FIG. 2 has a network topology as found in the United States.The data transmission network 1 comprises several line terminationdevices 2-1 to 2-N connected via lines 3-1 to 3-N to a switch 4 which isconnected via a line 5 to an IP backbone 6. Each line termination device2 is connected via a data transmission medium 7 through several networktermination devices 8-1 to 8-M, wherein in the example shown in FIG. 2,the number M of connected network termination devices is eight. The datatransmission medium 7 in the preferred embodiment as shown in FIG. 2 isan unshielded twisted pair of telephone lines (UTP) made of copper. Eachnetwork termination device 8-I is connected to a corresponding datacommunication device 9-I. The data communication devices are personalcomputers, IP telephones, laptops or television set-top boxes or anyother network equipment.

In the data transmission network 1 as shown in FIG. 2, the switch 4 isconnected to the IP backbone 6 and exchanges data with a very high dataexchange rate. The main switch 4 is e.g. an Ethernet switch to whichseveral line termination devices according to the present invention areconnected. The Ethernet switch 4 delivers the Ethernet packets to itsdestination according to a destination address. The Ethernet packets arebroadcasted by the line termination device as downstream data frames viathe transmission medium 7 to several network termination devices 8-1 to8-M in a downstream frequency band.

The downstream frequency band may in a VDSL application range between 1and 3 MHz. The Ethernet packets are broadcasted with a data transferrate of e.g. 15/20 MBPS. The network termination device 8-i receives thedata packet and transmits it to the corresponding data communicationdevice 9-i. Data coming from data communication device 9-i is sentwithin an upstream data frame via the data transmission medium 7 to thecorresponding line termination device 2.

There are three different possibilities for data transmission paths. Ina first data path, the network termination device 8-i sends an upstreamEthernet data frame to the corresponding line termination device 2 whichdelivers the data frame to the main switch 4. If the upstream frame isaddressed to another network termination device 8-j within the samegroup of network termination devices, the switch 4 sends the receivedupstream data frame as a downstream data frame via the line termination2 and the data transmission medium 7 to the addressed destinationnetwork termination device 8-j.

If the upstream data frame is addressed to a network termination device8-j within another group of network termination devices 8, the switch 4sends the received upstream data frame to the corresponding linetermination device 2-j of the destination network termination device 8-jwhich transmits it via another data transmission telephone line to theaddressed network termination device 8-j.

In a third possible data transmission path, the upstream data frame sentby a network termination device 8-j is destined for a remote networktermination device and will be delivered from switch 4 via line 5 to theIP backbone 6.

In the data transmission network shown in FIG. 2 according to theUS-topology, all network termination devices 8 within one group areconnected to the same telephone copper line 7. The network terminationdevices 8 may be distributed within a range of 100 m. A feeding linebetween the line termination device 2 and the different networktermination devices 8 may be in one building and may have a lengthbetween 0.5 and 1 km. The data transmission medium 7 in the form of theunshielded twisted pair telephone line made of copper is already wiredwithin the building and is used by the present invention also for xDSLdata transmission. Accordingly the data communication devices 9-i withinin the building may form a local area network (LAN) without the need toprovide a separate Ethernet cable structure.

FIG. 3 shows a data transmission network 1 having the topology as can befound in Europe and Asia. Several data communication devices 9-i areconnected by means of a network termination device 8-i and a datatransmission medium 7-i such as an unshielded twisted telephone line(UTP) to a corresponding low-pass filter 10-i within a central office 11and to a corresponding high-pass filter 12-i. The low-pass filters 10may have a cut off frequency between 8 kHz and 0.1 MHz for filteringvoice data, and the high-pass filters 12 may have a cut off frequencybetween 0.1 MHz and 0.7 MHz for filtering xDSL data signals. Eachlow-pass filter 10-i within the central office 11 is connected via aline 13-i to a telephone switch entry 14-i of a telephone switch 14. Thetelephone switch 14 is connected via a line 15 to an ordinary POTStelephone network 16.

The high-pass filters 12 are connected via lines 17 to a combiner 18which adds up the received high-pass filtered signals. The combiner 18is connected via line 19 to a line termination device 2. The linetermination device 2 is connected via line 3 to a main switch 4 which isconnected via line 5 to an IP backbone 6. In the data transmissionnetwork having the topology as shown in FIG. 3, a multi-port POTS/xDSLsplitter comprising the plurality of low-pass filters 10 and high-passfilters 12 is provided. The splitter filters the telephone signal on oneside and filters the xDSL signal on the other side.

FIG. 4 shows a block diagram of a line termination device 2 according toa preferred embodiment of the present invention.

The line termination device 2 comprises an xDSL transceiver 20 forbroadcasting downstream data frames to several network terminationdevices 8-I via the data transmission medium 7 and for receivingupstream data frames from the network termination devices 8-I via thedata transmission medium 7. The data medium 7 is e.g. an unshieldedtwisted pair telephone line UTP made of copper. The xDSL transceiver 20within the line termination device 2 comprises a line driver 21 fordriving the received signals and for driving signals to be transmitted.The line driver 21 is connected via a line 22 to a hybrid circuit 23which applies the received data signals via a line 24 to an analogreceiving filter 25 which is connected on the output side via a line 26to an amplifier unit 27 for amplifying the received and filtered datasignals. The amplified received signal is supplied via line 28 to ananalog/digital converter 29 which converts the received analog signal toa digital signal. The received digital signal is supplied via lines 30,31 to an automatic gain control circuit 32 controlling the amplifier 27via a control line 33 and to a digital QAM demodulator 34. The QAMdemodulator is connected on its output side via a line 35 to a digitalreceiving filter 36 for suppressing noise. The digital filter 36 isconnected via line 37 to an equalizer 38 for compensating determiningthe received data symbols. The slicer 40 is connected via line 41 to aQAM decoder 42 which generates from the detected data symbols thecorresponding data bits to be packed in a data frame. The QAM decoder 42is connected via line 43 to a TC deframer 44 which is connected via line45 to a deframer 46, e.g. an Ethernet deframer. The TC deframer 44distracts messages from the received upstream data frames and suppliesthem via a line 47 to an NT status memory 48. The deframer 46 isconnected via line 49 to an MII interface 50 for connecting the linetermination device 2 via a line 3 to a switch 4.

The MII interface 50 is connected via a line 51 to a framer 52, e.g. anEthernet framer. The Ethernet framer 52 is connected via line 53 to a TC(TC: Transparence Convergence) framer 54. The TC framer 54 is connectedvia line 55 to a QAM encoder 56 within the xDSL transceiver 20. The QAMencoder 56 is connected via line 57 to a digital transmitting filter 58.The filtered digital signal is supplied via line 59 to a digitalmodulator 60 which is connected on its output side via line 61 to adigital/analog converter 62. The modulated digital signal is convertedby the digital analog converter 62 to an analog signal which is suppliedvia line 63 to an analog filter 64. The filtered analog signal issupplied via line 65 through the hybrid circuit 23 and broadcasted viathe line driver 21 and the data transmission medium 7 to the networktermination devices 8-I.

The line termination device 2 comprises a selection unit 66 which isconnected via lines 67 to the NT status memory 48. The selection unit 66selects the network termination devices which have sent a requestmessage within an upstream data frame depending on the statusinformation data stored within the status storage means 48.

The line termination device 2 further comprises a grant messagegenerator 68 connected to the selection unit 66 via line 69. The grantgenerator 68 is connected via control line 70 to the TC framer unit 54.The selection unit 66 selects according to the information data storedwithin the storage means 48 a network termination device 8-j connectedto the line termination device 2 and activates the grant messagegenerator 68 for generating a data transmission grant message for theselected network termination device 8-i.

The selection unit 66 further controls via control lines 71, 72 an AGCrandom access memory 73 and an equalizer coefficient random accessmemory 74. In the AGC random access memory 73, the automatic gaincontrol coefficients for the different network termination devices 8-iof one group are stored. In the equalizer coefficient random accessmemory 74, the equalizer coefficients for the different networktermination devices 8-i within one group connected to the linetermination device are stored. The automatic gain control random accessmemory 73 stores the AGC coefficients via line 75 from the automaticgain control circuit 32 within the xDSL transceiver 20. The equalizercoefficient random access memory 74 stores the equalizer coefficients ofthe different network termination devices from the equalizer 38 via line76. The AGC coefficients of the selected network termination device areloaded into the automatic gain control circuit 32 via a line 77 inresponse to a control signal supplied by the selection unit 66 viacontrol line 71. The equalizer coefficients are loaded into theequalizer 38 via a line 78 in response to a control signal of theselection unit 66 delivered via control line 72.

The selection unit 66 reads the status information data stored withinthe NT status storing means 48 and selects the network terminationdevices 8-i for data transmission according to a programmed selectionalgorithm and activates the grant message generator 68 for generatinggrant messages for the selected network termination devices 8-i. Theselection of the network termination devices may be performed by anyselection scheme such as a priority scheme. In an alternativeembodiment, all network termination devices 8-i may have the samepriority.

FIG. 5 shows an example for a network termination device status tablestored within the storing means 48. Each network termination deviceconnected to the line termination device 2 has a unique networktermination device address. As status information, the status table maycontain the number of time slots required by the different networktermination devices 8-i for data transmission. This number is receivedby the line termination device 2 in an upstream data frame as a requestmessage. Any kind of further data information of the different networktermination devices 8-I may be stored in the status table which arenecessary for the selection algorithm.

FIG. 6 shows a block diagram of a preferred embodiment of a networktermination device 8 according to the present invention.

The network termination device 8 comprises an xDSL transceiver 20 havinga similar structure as the xDSL transceiver 20 in the line terminationdevice. Additionally the network termination device 8 comprises a timingcircuit 78 for tracking the timing of the clock signal of the linetermination device 2. The timing circuit 78 is provided forsynchronizing on the line termination device master clock. The timingcircuit 78 is connected via line 79 through a voltage controller circuit80 controlling a voltage controlled oscillator 81 via control line 82,the voltage controlled oscillator 81 generating an internal clock signalfor the network termination device.

The network termination device 8 further comprises a network terminationdevice status generator 83 generating any kind of status informationdata describing the status of the network termination device. The NTstatus generator 83 generates messages which contain information aboutthe network termination device, and In particular how many time slotsfor data transmission are required by the network termination device.The generated request message is transmitted via a line 84 to the TCframer 54 and put into a message field within an upstream data frame tobe sent to the line termination device by the xDSL transceiver 20.

In the transmitting path of the xDSL transceiver 20 of the networktermination device 8 there is provided an additional switch 85controlled by a grant decoder 86 via a control line 87. When sendingdata information, switch 85 is closed. The request message generator 83generates a data transmission request message when the datacommunication device 9 connected to the network termination device 8contains a buffer memory for buffering data sent from the datacommunication device 9 when a request for data communication is notgranted by the line termination device 2 immediately.

The grant message decoder 86 is connected via line 88 to the TC deframer44 and decodes the messages within a message field of the receiveddownstream data frames broadcasted by the line termination device 2 viathe data communication medium 7. In case that the grant decoder 86decodes a grant message addressed to the specific network terminationdevice 8-i it sends a control signal via the control line 87+0 to theswitch 85 and the buffered data coming from the corresponding datacommunication device 9-i connected to the network termination device 8-iare transmitted to the line termination device 2 via the datacommunication medium 7 which is preferably an unshielded twisted pairtelephone line.

The TC framer 54 within the line termination device and the networktermination device may also contain a Reed-Solomon-correction unit, ascrambler and an interleaver.

FIG. 7 a shows a request message transmitted from a network terminationdevice 8 upstream to a line termination device 2 in principle. Therequest message which is put into a message field of an upstream dataframe contains a request message opcode which may be recognized by theTC deframer unit 44 within the line termination device 2. The requestmessage further includes a number of time slots which are required fordata transmission by the network termination device 8 which sends therequest message.

FIG. 7 b shows a grant message in principle. The grant message containsa grant message opcode which may be recognized by a grant messagedecoder 86 within a network termination device 8. The grant messagefurther contains the MAC address of the destination network terminationdevice 8.

FIG. 8 shows a flowchart for describing the operation within a linetermination device 2 in principle.

After a start step S0, the line termination device 2 receives in a stepS1 upstream data frames from all corresponding network terminationdevices 8-i connected to the line termination device 2 via the datatransmission medium 7. The network termination devices 8-i are scheduledby the line termination device 2.

If the received upstream data frames contain data transmission requestmessages, the TC deframer 44 of the line termination device 2 stores thenumber of time slots requested by the network termination device intothe NT status table of memory 48 in a step S2.

In step S3, the selection unit 66 selects at least one networktermination device 8-i according to programmed selection criteriaaccording to a given priority or to urgency of data transmission.

In a further step S4, the grant message generator 68 is activated by theselection unit 66 and generates a grant message addressed to theselected network termination device 8-i.

In a step S5, the line termination device 2 broadcasts downstream dataframes to all network termination devices 8-i connected to the linetermination device 2 via the telephone line 7. The broadcasteddownstream data frames include payload data to be transmitted from theline termination device 2 to the network termination devices 8 and fromthere to the corresponding data communication devices 9 such ascomputers, laptops or IP phones. Further data frames include thegenerated grant messages, i.e. the grant message opcode and theMAC-addresses of the selected network termination devices 8.

In a further step S6, the AGC coefficients stored in the memory 73 andthe equalizer coefficients stored in the memory 74 are loaded into theautomatic gain control circuit 32 and into the equalizer 38 of the xDSLtransceiver 20 within the line termination device 2.

In a further step S7, the line termination device 2 waits for determinedresponse time for the response from the network termination devices 8.

FIG. 9 shows the further flowchart for describing the operation withinthe network termination device 8-I according to the present invention.After a start step S0, the network termination device 8 receives a datastream broadcasted from the line termination device 2 via the datatransmission medium 7 in a step S1. The messages within the messagefields of the received downstream data frames are decoded by the decoder86 within the network termination device 8 in a step S2.

In a further step S3, it is decided whether the received message is agrant message for the specific network termination device 8 or not. Incase that the network termination device did not receive a grantmessage, it further monitors the data frames broadcasted by thecorresponding line termination device 2.

In case that the network termination device 8 has received a grantmessage from the line termination device 2, it transmits in a step S4several upstream data frames to the line termination device 2 via thedata transmission medium 7. The number of the transmitted upstream dataframes depends on the number of time slots allocated by the linetermination device 2 for data transmission. The upstream data streamsinclude payload data to be transmitted from the line termination device2 via switch 4 to further line termination devices 2 or to the backbone5 or to other network termination devices 8 within the same group.Further, the upstream data frames include status data indicating theactual status of the network termination device 8-i, e.g. acceptablewaiting time for receiving grant messages. Further, the upstream dataframe sent by the network termination device 8 may contain furthermessages, such as a further request message containing a request messageopcode and number of time slots required for further data transmission.

The line termination device 2 comprises an xDSL transceiver having a MACfunctionality and acts as the master of the point to multi-point datalink. The line termination device 2 schedules each network terminationdevice 8 on a TDD basis. In a European or Asian network topology, apassive signal splitter is provided in order to combine the xDSL signalof different users on one copper line.

The network termination device 8 comprises an xDSL transceivertransmitting data according to the request received from the master,i.e. a line termination device 2.

On the downstream frequency band, a sustained signal is transmittedpermanently from the line termination device 2, i.e. the linetermination device 2 broadcasts all the time downstream data frames.This has the advantage that all network termination devices 8 keep beingsynchronized to the downstream signal. Each network termination device 8transmits its upstream signal when getting a grant on the messagechannel. The transmission is performed for a granted period of time.

With the invention it is possible using a well-proven xDSL-QAMtransceiver for the physical layer over the target infrastructure whichis e.g. a telephone line (CAT3). Using a TDM media access control on theupstream side and broadcasting of data frames on the downstream has theadvantage that the xDSL transceiver has a reduced synchronization timeon the upstream. Using an xDSL transceiver makes the system according tothe present invention compliant with other xDSL systems.

The data transmission is carried on a signal copper line, upstream anddownstream, wherein the copper line may be shared by at least eightusers. Since the line termination device 2 works as a master, nocollision base MAC is required and all network communication devices arefully synchronized. The data transmission network may be implementedeither in a US-topology or European/Asian topology. The datatransmission network according to the present invention takes advantageof the current asymmetric application demand and is compatible with10BaseS. Possible applications are fast Internet, game on demand,netgames, centric services, MPEG-4 VOD.

In a preferred embodiment, the messages are protected with CRC. In casethat an error is detected in one message, the message may be discarded.Some important messages may be transmitted up to three times in order toensure their reception. The grant message has to have a minimal responsetime.

The line termination device 2 keeps the last equalizer coefficients andACG coefficients of each network termination device 8 connected to theline termination device 2. The line termination device 2 reloads thecoefficients to its xDSL transceiver while awaiting the relevant NTsignal. In order to avoid reflections on the data transmission medium,the impedances of the different network termination devices 8 arebalanced.

1. Data transmission network having at least one line termination deviceconnected via a telephone line wired within a building to severalnetwork termination devices, wherein each network termination device isconnected to a corresponding data communication device to form a localarea network (LAN) comprising: a request message generator forgenerating a data transmission request message when the datacommunication device connected to the network termination device issending data, wherein a data transmission request message comprises arequest for data transmission of the data sent by the data transmissiondevice, and an xDSL transceiver for transmitting an upstream data frameincluding the generated request message via the telephone line to theline termination device, the line termination device comprising: aselection unit for selecting network termination devices which have senta data transmission request message depending on status information dataof the network termination devices stored in storing devices of the linetermination devices, wherein the status information includes addressesof the network termination devices and corresponding numbers of therequired time slots received from the network termination devices indata transmission request messages, a grant message generator forgenerating data transmission grant messages for the selected networktermination devices, wherein each data transmission grant messagecomprises a grant message opcode and an address of the selected networktermination device, and an xDSL transceiver for broadcasting downstreamdata frames including the generated grant messages via the telephoneline to the network termination devices.
 2. Data transmission networkaccording to claim 1, wherein the upstream data frames are sent from thenetwork termination device to the line termination device via thetelephone line in an upstream frequency band, and the downstream dataframes are sent from the line termination device to the networktermination device via the telephone line in a downstream frequencyband.
 3. Data transmission network according to claim 2, wherein thedownstream frequency band ranges between 1 and 3 MHz and the upstreamfrequency band ranges between 4 and 8 MHz.
 4. Data transmission networkaccording to claim 1, wherein each line termination device comprises anMII interface for the connection to a switch.
 5. Data transmissionnetwork according to claim 1, wherein each data frame comprises: asynchronization data field, a message data field, a payload data field,and an error correction data field.
 6. Data transmission networkaccording to claim 1, wherein each network termination device isconnected to a passive signal splitter.
 7. Data transmission networkaccording to claim 6, wherein the passive signal splitter comprises alow-pass filter for filtering a telephone signal, and a high-pass filterfor filtering an xDSL data signal.
 8. Data transmission networkaccording to claim 1, wherein the selection unit reads the statusinformation data stored in the storing means, selects the networktermination devices for data transmission according to a programmedselection algorithm, and activates the grant message generator forgenerating grant messages for the selected network termination devices.9. Data transmission network according to claim 1, wherein the xDSLtransceiver of the line termination device includes an adaptiveautomatic gain control circuit and an equalizer.
 10. Data transmissionnetwork according to claim 1, wherein the line termination devicecomprises a first storing means for storing AGC coefficients for thenetwork termination devices connected to the line termination device,and a second storing means for storing equalizer coefficients for thenetwork termination devices connected to the line termination device.11. Data transmission network according to claim 10, wherein the AGCcoefficients of the selected network termination device selected by theselecting unit are loaded into the AGC circuit of the xDSL transceiverof the line termination device.
 12. Data transmission network accordingto claim 10, wherein the equalizer coefficients of the selected networktermination device selected by the selecting unit are loaded into theequalizer of the xDSL transceiver of the line termination device. 13.Data transmission network according to claim 1, wherein the networktermination device comprises a grant decoder for decoding messageswithin downstream data frames broadcasted by the line terminationdevice.
 14. Data transmission network according to claim 1, wherein thexDSL transceivers are VDSL transceivers.
 15. Data transmission networkaccording to claim 1, wherein the impedances of the network terminationdevices connected to the data transmission medium are balanced.
 16. Datatransmission network according to claim 1, wherein eight networktermination devices are connected via the data transmission medium tothe line termination device.
 17. Data transmission network according toclaim 1, wherein several line termination devices are connected to aswitch.
 18. Data transmission network according to claim 17, wherein theswitch is connected to an IP backbone.
 19. Method for data transmissioncomprising: generating a data transmission request message by a networktermination device when the network termination device receives datafrom a connected data communication device, wherein a data transmissionrequest message comprises a request message opcode and a number of timeslots required for data transmission of the data sent by the datacommunication device; transmitting the generated data transmissionrequest message within an upstream data frame via a telephone line wiredwithin a building to a line termination device; selecting the networktermination devices depending on stored status information data of thenetwork termination devices, wherein the status data includes addressesof the network termination devices and corresponding numbers of therequired time slots received from the network termination device in datatransmission request messages; generating data transmission grantmessages for the selected network termination devices by the linetermination device, wherein each data transmission grant messagecomprises a grant message opcode and an address of the selected networktermination device; broadcasting downstream data frames containing thegenerated grant messages via the telephone line to the connected networktermination devices; and transmitting data from the selected networktermination device after the grant message has been decoded.